jbsu32 jbsu32 - 3 months ago 9
Bash Question

In bash how do I divide two variables and output the answer rounded upto 5 decimal digits?

I took two variables as input and after dividing them, I want to get the output rounded up to 5 decimal digits. I have tried this way ->

sum=12
n=7
output=$("scale=5;sum/n"|bc)
echo $output


My code isn't showing any output. What can I do??

TestCase:

If
sum=3345699
and
n=1000000
then
(sum/n)=3.345699
, it should be changed into
3.34570
.

Answer

The problem here is that you missed the echo (or printf or any other thing) to provide the data to bc:

$ echo "scale=5; 12/7" | bc
1.71428

Also, as noted by cnicutar in comments, you need to use $ to refer to the variables. sum is a string, $sum is the value of the variable sum.
All together, your snippet should be like:

sum=12
n=7
output=$(echo "scale=5;$sum/$n" | bc)
echo "$output"

This returns 1.71428.

Otherwise, with "scale=5;sum/n"|bc you are just piping an assignment and makes bc fail:

$ "scale=5;sum/n"|bc
bash: scale=5;sum/n: No such file or directory

You then say that you want to have the result rounded, which does not happen right now:

$ sum=3345699
$ n=1000000
$ echo "scale=5;($sum/$n)" | bc
3.34569

This needs a different approach, since bc does not round. You can use printf together with %.Xf to round to X decimal numbers, which does:

$ printf "%.5f" "$(echo "scale=10;$sum/$n" | bc)"
3.34570

See I give it a big scale, so that then printf has decimals numbers enough to round properly.